Devices that operate with catalytic measuring elements to perform gas measurements have been used in gas measuring engineering applications. In particular, pellistors are widely used for in gas measuring engineering applications.
General conditions must be taken into account when such measuring elements are used. These conditions arise from the fact that the electric properties of such catalytic measuring elements may change during the measurement. Also, they are possibly used in the presence of an explosion hazard.
The pellistors are considered to be semiconductor elements especially in conventional circuits with pellistors. Since the resistance of these pellistors may change substantially as a function of the temperature, protective resistors and thermal safety devices are usually used to limit the maximum power of the pellistor and at the same time to limit the maximum current to values at which ignition by spark is ruled out in an environment with explosion hazard.
The drawback of such a circuit is, however, that both a protective resistor and a thermal safety device represent separate users and they consume electric power. This represents a considerable drawback, especially in case of portable devices that are battery-operated. The use time is substantially reduced in this manner. Consequently, more energy must be made available than would be necessary for the operation of the pellistor alone. The energy storage means necessary for this, for example, batteries, increase the weight of such devices in a disadvantageous manner.